My friend just stopped talking to me?

I have been friends with this girl for 10 years. We are both 20. A week ago, she just stopped talking to me. Usually she texts me and calls me everyday, but last week, she just stopped. I texted her last week, asking her if she is okay and if there's anything bothering her, and she said that she was fine. But I don't know why she just stopped talking to me.

I don't think that she is exactly mad at me, because we are taking a summer college class together, and today she said hi to me, but that was about it.

I am also leaving for college in a little over a month, and would like to spend time with her before I leave, but I really don't know why she stopped talking to me.